The two most important viral pathogens, based on mortality in the United States are HIV and influenza. The overall goal of this 5 year research plan is to test the hypothesis: ?9-tetrahydrocannbinol (?9-THC) attenuates antiviral responses against HIV and influenza virus through impairment of CD4+ T cell activation and function, and elicitation of antiviral specific CD8+ T cell effectors through CB1/CB2-dependent and -independent mechanisms. Our findings show that ?9-THC markedly impairs: (a) host resistance to influenza infection as evidenced by increased lung viral burden and decreased CD4+ and CD8+ T cell effectors; and (b) CD8+ T cell function, cytotoxic T lymphocyte activity and interferon 3 productions in vitro, in response to HIV gp120 and influenza-associated PB1. In addition, we show that cannabinoid treatment suppresses T cell function by impairing T cell activation via a mechanism involving rapid and sustained elevation in intracellular calcium [Ca+2]i, leading to T cell anergy. The rise in [Ca+2]i levels causes deregulation of the nuclear factor of activated T cells (NFAT) and impairs transcription of interleukin-2 and other NFAT-regulated cytokines. Additional results show that CB1-/-/CB2-/- mice are markedly more efficient in clearing influenza virus than wild type mice implicating a role for CB1 and/or CB2 in viral host resistance. Based on the above findings we will test our hypothesis using novel cell-based models with the following specific aims (SA): SA1 is to characterize impairment by ?9-THC, and the involvement of CB1/CB2, on the elicitation of antigen-specific multifunctional CD8+ T cells in response to HIV gp120 and influenza-associated PB1; SA2 is to characterize the impairment by ?9-THC, and the involvement of CB1/CB2, on CD4+ T cell activation and function induced by HIV gp120 and influenza-associated PB1; SA3 is in an in vivo surrogate model of HIV and influenza challenge, to characterize the impairment by ?9-THC, and involvement of CB1/CB2, on the elicitation of antigen-specific multifunctional CD8+ T cell responses to HIV gp120 and influenza-associated PB1; SA4 is in an in vivo surrogate model of HIV and influenza challenge, to characterize the impairment by ?9-THC, and involvement of CB1/CB2, on the CD4+ T cell response to HIV gp120 and influenza PB1; and SA5 is to determine the effect of 9-THC on the generation of multifunctional human peripheral blood (HPB) CD8+ T cells in response to HIV gp120 and influenza-associated M1. The significance of the proposed studies is that in their immunocompromised state, those infected with HIV or cancer patients are especially susceptible to infectious pathogens including influenza. Moreover, HIV and cancer patients are well known users of cannabis for stimulating appetite to alleviate the wasting syndrome that accompanies AIDS and as an antiemetic to relieve the nausea produced by cancer chemotherapy. In spite of the many HIV and cancer patients utilizing cannabis multiple times daily, an important data gap concerns the extent to which this practice may lead to a further diminution in immune competence and a more rapid progression of disease or mortality due to secondary infections.